Electric instrument relay



"April 10, 1945. M SNELL ELECTRIC INSTRUMENT RELAY Filed April 6, 1942 Patented Apr. 10, 1945 ELECTRIC INSTRUMENT RELAY Maurice Saxon Snell, Enfield, England, assignor to Sangamo Electric Company, Springfield, 111., a corporation of Illinois Application April 6, 1942, Serial No. 437,879 In Great Britain April 18, 1941 10 Claims.

This invention relates to electrical instrument relays and particularly to sensitiveinstrument relays of the type including magnetic contacts that insure reliable non-chattering contact closures.

Some form ofresetting mechanism is required in a sensitive relay of this type as the torque developed by the control current is usually of an order substantially lower than the force resulting from the magnetic attraction of the engaged magnetic contacts. Various pusher arm mechanisms have been employed to .reset the contact arm of a magnetic contact type relay, and it has also been proposed to effect the resetting by current flow through a coil surrounding the permanent magnet contact. rent flow and the sense of the coil winding were so related that the resetting magnetic field neutralized the field of the permanent magnet cntact. A close regulation of the current flow through the resetting coil was essential to develop sufficient force for resetting the relay contact arm without, however, reducing the strength of the permanent magnet contact. A current flow just suflicient to neutralize the permanent magnet fleld will not eliminate all magnetic attraction since the soft iron contact will retain some The direction of curslight residual field after its first engagement with the permanent magnet contact. Fluctuations in the circuit resistance and in the voltage of the resetting current source made it advisable to design the prior electromagnetic resetting system for something more than an exact compensation of the field of the permanent magnet contact, but this design resulted in a progressive aging or loss in strength ,of the permanent magnet contact.

An object of the present invention is to provide an electrical instrument relay with magnetic contacts and with an electromagnetic resetting system of novel design that is positive in operation withoutaffecting the characteristics of the permanent magnet contact. An object is to provide a relay of the magnetic contact type that includes at least one soft iron contact and aresetting coil about the soft iron contact. An object is to provide asensitive instrument relav. that includes a magnetized contact cooperating with a soft iron contact to insure good contact closures. and a resetting system comprising a coil about the soft iron contact for establishing a resetting magnetic force in. opposition to the magnetic field of the magnetized contact,

netic. contact 4.

specification when taken with the accompanying I drawing in which Figs. 1 to 4, inclusive,.are fra mentary schematic views of electrical instrument.

mounting of the contact 5 upon a plate I with relatively long slots 8 for receiving the screws 9 that secure the plate to the base, not shown, of the relay. The plate 1 is so adjusted that the magnetic attraction between contacts 4, 5 will draw the contacts into engagement when the current flow through the relay coil 2 dropsto such value that the pointer 3 is moved counterclockwise, from its illustrated position, to aline with a desired scale graduation, for example the Engagement of the. relay congraduation a, tacts completes acircuit through the contacts, a currentsource I0 and a load I! that may be a motor device or a power relay for closing a load circuit. a

In accordance with this invention, the relay may be reset after a closure of the contacts by momentarily establishing an electromagnetic field opposed to the polarity of the field of the permanent magnet contact 4. A coil or winding 12 surrounds the soft iron contact 5, and is connected to a low voltage direct current source l3 by a switch l4 that may be operated manually or, as shown, by a relay II in the circuit that is completed by the relay contacts. The

relay I5 is relatively slow-acting to permit the intended operation of the load device H before the relay contacts are separated.

The polarity of the battery l3 and the winding of the coil l2 are such that current flow through the coil establishes magnetic repulsive force between the electromagnet contact 5 and the mag- The electrom'agnet magnetic field may be, and preferably is, somewhat stronger than the field of the permanent magnet 4 to effect a positive separation of the contacts independently of the torque established by current flow through the relay coil 2. The circuit design is not critical and the only essential requirement is that the coil l2 must have a-suflicient number 'of turns to create an over neutralizing magnetic field under the most adverse of normal operating conditions, i. e.- at the minimum exp'ectedvoltage of current source l3 and the maximum expected resistance of the resetting circuit. The coil l2 preferably includes somewhat more than the computed minimum number of turns as no damage results when the resetting magnetic field i sub-- stantiallystronger than the field of the permanent magnet contact 4. The permanent magnet 4 is not within the field of the resetting coil l2,

and the strength of the magnet contact 4 therefore is not adversely affected by a relatively high strength of the magnet field of the electromagnet 5, l2.

The circuit connections are simplified when the soft iron contact 5 and coil l2 are mounted on the relay base but it will be apparent that the .cations of the magnetized and soft ironcontacts may be reversed.

The magnetized contact of the relay may be an electromagnet according to the embodiment of the invention that is illustrated in Fig. 2. The contact 5 and coil I! may be identical with the Fig. l embodiment but the coil is normally connected to the current source l3 by the switch l4 that is opened by the relay I5 upon a closure ofthe relay contacts. The relay contact armor pointer 3 carries a soft iron rider I6 for coopiron contacts to limit the range of pointer displacement over which the movable contact is affected by the flow of current through a resetting v a relativelystationary contact, both contacts being of magnetic material and one being magnetized to attract the other upon displacement of said moving system to bring the contacts into proximity, and electromagnetic means for resetting said relay after a contact closure; said resetting means comprising a coil and direct current source for magnetizing said other .contact to establish a magnetic field in opposition to the magnetic field 'of the magnetized contact, and a switch in circuit with said coil and current source.

2. In an electrical instrument relay, the invention as recited in claim 1, wherein said magnetize ized contact is a permanent magnet.

eration with the magnetized contact 5. -The electromagnetic contact 5, I2 is deenergized upon aclosure of the relay contacts, and the residual magnetism of the contact system is overcome by a light coil spring II that surrounds the'tip of the contact 5 and is supported from the base plate I.

The strength of the spring I! is so selected thatv it does not prevent a reliable contact engagement so long as current fiows through the coil l2.

. Both relay contacts may be of soft iron, or other material of low retentivity, and provided with magnetizing coils according to the embodiment that is illustrated in Fig. -3. The relay pointer 3 carries a small soft iron rider 5' within a coil l2 that is energized from the current source l3. The stationary contact 5 and its coil l2 may be substantially as previously described, the coils I2, I 2 being connected to the-current source in such manner that the contacts 5, 5' are normally magnetized in an attractive sense. A polarity reversing switch 18 is arranged between the current source and one of the'magnetizing coils l2,

I! for automatic or manual operation to reset the relay.

For simplicity of illustration, the relays of Figs. 1-3 have been shown as of the single closure type but it will be apparent that the. described constructions may be applied to instrument relays in which the contact'arm moves between low and high contacts. A double closure relay system with contacts of thegeneral type of- Fig. 1 is shown in Fig. 4, the controlled relay circuit being omitted for simplicity and the resetting circuit being illustrated as including 'a manually operated switch Ma. The low contact 5 and associated elements may be identical with the corresponding elements of 1, and the high" contact system comprises a similar assembly of a contact 5h 'of 3. In an electrical instrument relay, the invention as recited in claim 1, wherein said magnetized contact is an electromagnet.

4. In an electrical instrument relay, the'invention as recited in claim 1, wherein both of said contacts are elect'romagnets energized from said current source, and said switch is a'polarity reversing switch for reversing the direction of current flow through said coil to magnetize said other contact to attract or alternatively to repel the first contact.

5. In an electrical instrument relay of the magnetic pull-in type, the combination with a moving system carrying a permanent magnet. contact for cooperation with a stationary contact,

- of said switch to energizesaid electromagnetic means.

6. In an electrical instrument relay, the invention as recited in claim 5, in combination with circuit means including said relay contacts for automatically closing said switch upon an engagement of said permanent magnet contact with the cooperating contact.

'7. In an electrical instrument relay, a moving system carrying a permanent magnet contact for cooperation with a relatively stationary contact of magnetic material of low retentivity, a coil surl rounding said stationary contact, and a resetting low retentivity, a coil l2h on the contact 511., and an adjustable plate In supporting the contact 5h.

The sense of the windings of coils l3, 12h and the direction of current flow through the coils are such that the fields setup by a closure of the switch He will repulse the magnetized contact 4 fromthe' contacts 5, 511.. In the case of relays in a which the high-low contacts 5h, 5 may be adjusted into relatively close proximity, soft iron yokes or housings may be provided for the soft circuit including a direct current source and switch .in series circuit with said coil.

8. In an electrical instrument relay, a moving system carrying a contact, a cooperating rela-' tively stationary contact, both contacts being'of magnetic material and one con'tactbeing of low retentivity, a coilsurrounding said'contact-of low retentivity magnetic material, a direct current source in .circuit with said coil to magnetize the associated contact to attract the other contact, and relay resetting means for interrupting current flow to said coil and positively overcomaaraaoa ing the residual magnetic attraction between the contacts.

9. In an electrical instrument relay, the invention as recited in claim 8, wherein said other contact is a body of magnetic material of low retentivity surrounded by a coil connected to a direct current source, and said resetting means includes a polarity reversing switch for reversing the direction 01' current flow through said first coil.

10. In an electrical instrument relay, a moving I system including a contact arm carrying a miniature permanent magnet contact, a pair of cooperating relatively stationary contacts or soft iron at opposite sides of said contact arm for cooperation with said permanent magnet contact, and resetting means for said relay; said means including coils surrounding said soft iron contacts, a direct current source, and switch means for connecting a coil to said current source after an engagement of said permanent magnet contact with the soft iron contact associated with that coil, the directions of current flow through the respective coils establishing electromagnetic fields in opposition to the field of the permanent magnet contact.

MAURICE SAXON SNELL. 

